Koji Tada

Crystal Growth and Superconductivity of Tl-Ca-Ba-Cu-O System

Single crystals of oxides in the Tl-Ca-Ba-Cu-O system with the general formula Tl2Can-1Ba2CunOx (n=1, 2, 3, 4) have been successfully grown by the flux method. All crystals were of the platelet form ranging from 0.6 to 5 mm2. The transition temperatures of as-grown crystals, determined by DC SQUID magnetometer, were 84 K, 110 K, and 118 K for n=1, 2, and 3, respectively, but slightly lower for 115 K, where n=4. The results of the differential thermal analysis (DTA), X-ray diffraction measurement and energy dispersive X-ray microanalysis (EDX) will be also reported.

Properties of high Jc BiSrCaCuO and TlBaCaCuO thin film

Abstract BiSrCaCuO thin films were prepared by an RF magnetron sputtering. We obtained a c-axis oriented polycrystal with many intergrowth layers. This film has high Jc of 3.4MA/cm 2 at 77.3K. TlBaCaCuO thin films were also prepared by the sputtering. It was a c-axis textured polycrystalline thin film. Its Tc(R=0) and Jc was 115K and 3.2MA/cm 2 , respectively.

Preparation of Alkaline-Metal-Doped C60 Superconducting Film and Its Stabilization in Air with Protective Coatings

Preparation conditions of C60 film were studied by varying substrates, substrate temperature and the rate of evaporation. Crystalline C60 thin films were prepared on GaAs(100) at the substrate temperature of 100° C in order to obtain superconductors by alkaline metal doping. The Rb/Cs-doped film showed a superconducting transition with T c( onset)=24±3 K and T c( zero)=8 K. The composition of the superconducting film was measured by micro-Auger electron spectroscopy. Air stability of Rb3C60 superconducting film with protective coatings applied was studied. A Si protective film maintained superconductivity for 220 min in air. In addition a Si/Al protective coatings maintained superconductivity for 8 h.

Superconductivity on Single Crystals of Tl-Ca-Ba-Cu-O System

The investigation on the growth of single crystals of the Tl-Ca-Ba-Cu-0 superconducting system was carried out using the flux growth method. The crystal structure and superconducting properties of mm-sized single crystals were measured using X-ray diffraction and the SQUID magnetometer. The grown crystals are typically in platelet form ; 0.5 to 2.5 mm wide and about 0.2 mm thick. The crystals exhibit a mirror-like surface and some growth steps can be observed through a scanning electron microscope. The superconducting onset transition temperature of 108K to 118K was determined by DC magnetic susceptibility obtained for as-grown single crystals. The transition temperature has a tendency to increase as the amount of CaO-CuO in the starting nominal composition rises. According to the X-ray diffraction measurement, the c-axis of the grown crystals is 35.8A for those with Tc of 118K, and 29.3A for those with Tc of 108K.

Chapter 5 InP Substrates: Production and Quality Control

Publisher Summary This chapter presents a discussion on the production and quality control of indium phosphide (InP) substrates. It describes the techniques related to InP single crystal materials and their characterization. The applications of InP crystals and the requirements for their quality is described in the chapter. The chapter reviews the details of crystal growth techniques, including recent developments obtained in laboratories. The techniques used in the evaluation, quality control, and wafer processing are also described in the chapter. InP single crystals have been used exclusively as conductive substrates for infrared optical devices. They are also under development as semi-insulating substrates usable in higher frequency microwave devices, such as metal–insulator–semiconductor field-effect transistor (MISFETs) and optoelectronic integrated circuits. There is a great demand for the development of higher quality indium phosphide single crystals. For this purpose, the technologies reviewed in the chapter, especially those concerning both the crystal growth and the processing of this material, are very important for future developments. Etch-pit density (EPD) is one of the best indicators of the quality of II–-V semiconductor crystals.

Structural Study of Tl2Ca3Ba2Cu4Ox Single Crystal by Transmission Electron Microscopy

The microstructure of Tl2Ca3Ba2Cu4Ox (2324-phase) single crystals grown by the slow-cooling method was investigated using transmission microscopy. These single crystals showed superconducting onset transition temperatures of 113 to 115 K, and lattice constants were a=b=3.85 A and c=42.0 A by X-ray diffraction measurement. The high-resolution transmission electron microscopy (TEM) observations revealed intergrowths of Tl-O single-layered structures, 1324 and 1425, with stacking spacings of 19 A and 22 A, in addition to a 2223 phase of 36 A.

Magnetic-Field Angle Dependence of The Critical Current Density in Bi-2223 Superconducting Tape

Critical current densities (Jc) have been investigated in Ag — sheathed Bi-2223 superconducting tapes which were prepared by powder-in-tube technique. The Jc was measured in terms of both magnitude (B) and angle (Θ) to the tape surface of the magnetic field. In the high angle range, that is, the magnetic field component perpendicular to the tape surface (BsinΘ) was large, Jc values were able to be expressed by one universal function independently of the magnitude of the magnetic field. That function was proportional to the logarithm of BsinΘ (i.e., Jc ∝ log(BsinΘ)). Jc values were out of that function when the angle was decreased and saturated in the range near Θ = 0. The angles at which Jc began to part from the above function hardly depended on the magnitude of magnetic field. It was considered that the Jc of the sample was basically dominated by the magnetic field component perpendicular to the tape surface, that is, parallel to the c-axis of the crystal structure. The suppression of Jc in the low angle range may be due to misaligned grains. The misaligned angle was investigated by SEM. It was estimated that the mean misalignment angle was about 10°.

Stabilization of Rb 3 C 60 Superconducting Film in Air

The air stability of Rb3C60 superconducting film was studied with applying protective coatings. Rb3C60 superconducting thin film was prepared with vacuum deposition equipment using the conventional method. The protective film was deposited on the Rb3C60 film using the electron beam method. The sample with a Si protective film shows superconducting transition at TC(onset) =24K, TC (zero)=10K. Si protective film maintained superconductivity for 220 minutes in air. In addition Si/Al double protective coatings maintained superconductivity for 8 hours.

Preparation of the Tl-Bi-Sr-Ca-Cu-O Superconducting Thin Film

Thin films of (Tl, Bi) Sr2CaCu2Ox (1212 phase) and (Tl, Bi) Sr2Ca2Cu3Ox (1223 phase) with single Tl-O layered structures were prepared using a two-step process which involved a deposition of film followed by annealing under a thallium oxide vapor. When the films were annealed at 800–860°C, crystallization from the amorphous to 1212 phase occurred, and at 920°C, the 1223 phase was mainly formed. The highest zero resistivity temperature of the 1223 film was 109K. According to the TEM observation, films of both the 1212 and 1223 phase were almost c-axis oriented and some intergrowth of the 1212 phase was seen in the 1223 phase.

Alkaline Metals Doping into C60 Thin Films

C60 thin films were prepared on GaAs(100) and quartz substrates by two different vapour deposition methods. Rb and Cs were found to be doped in crystalline C60 thin films by the resistance measurement during the course of the doping experiment. The Rb/Cs-doped film showed a superconducting transition at Tc(onset)=24±3 K and Tc(zero)=8 K. The composition of the superconducting film was investigated by µ-Auger Electron Spectroscopy (µ -AES). This is the first confirmation of superconductivity in a Cs/Rb-doped Cgo thin film.